Molded plastic parts with molded-in threaded bores often require the thread/bore diameter to be verified for consistency before the molded parts are shipped for assembly with mating threaded parts. Bore and thread gauges are known, but while useful for gauging the open ends of the bore, are generally not practical for measuring inconsistencies along the full length of relatively small diameter bores in large numbers of parts. Molded bores in both thermoplastic and thermosetting plastic materials often tend to “hourglass” or constrict adjacent thicker areas of the part that create heat sinks affecting the cooling rate along the bore. If tolerances are strict, the need for full-length bore verification in parts prone to this problem becomes important. Moreover, bore gauges only diagnose the problem.
It has been known to use a specially machined threaded tap (or one of the mating parts, modified to cut) to verify and “chase” or remove extra material from the bore by attaching the tap to a hand drill and running it manually through the bore.